The present invention relates to a control system and method for regeneration braking of an electric vehicle, and more particularly to regeneration brake control for an electric vehicle having, a battery and an alternating current motor.
A conventional control method for regeneration braking of a vehicle is disclosed in Japanese Patent Application Laid-Open No.1-126103 (1989). According to that method, regeneration braking by a motor is actuated prior to mechanical braking to effectively recover regeneration energy to a battery by surely working the regeneration braking.
However, in the prior technique described above, there are some cases where the battery does not have the capability of receiving the regeneration energy, and consequently the regeneration braking force is insufficient depending on the state of the battery. As a result, the required braking force cannot be obtained. The cases arise when, for example, the battery is over-charged. In this case, since the battery is in a state in which it is incapable of receiving further energy, the battery does not accept the regeneration energy even though the battery is allowed to recover regeneration energy. As described above, when the battery is unfortunately in an over-charged state during braking, the require force of regeneration braking may not be obtained.
Further, in another known control method for regeneration braking of an electric vehicle, the surplus regeneration energy is consumed by providing a resistance and a switching element on the vehicle. In order to sufficiently consume the regeneration energy by this method, however, it is necessary to provide a resistance and switching element having a large wattage, which leads to an increase in the weight of the electric vehicle and brings about bad effects in the performance and the cost of the vehicle.
Furthermore, there is a disadvantage in that it is difficult to properly design the wattage of the resistance since the regeneration energy changes depending on the driving condition of the vehicle, which raises a problem concerning reliability of the system.